1. Field of the Invention
The present invention relates generally to handling of nuclear fuel pellets and, more particularly, is concerned with an apparatus and method for unloading pellets from a sintering boat into a pellet transfer pan.
2. Description of the Prior Art
Conventional practice in fabrication of nuclear fuel pellets requires transfer of pellets from station to station in the manufacturing process. Heretofore, transfer between certain stations has been performed manually. For instance, pellets are typically sintered in a furnace while stacked in large numbers in a boat, a square-shaped molybdenum container with an open top. Following the sintering station, the pellets must be unloaded from the boat into a tray or pan for transport to another pellet processing station, such as a grinding station.
Since the pellets are hard, abrasive and subject to chipping on impact and since the molybdenum boat becomes brittle with continued service, it has been common practice to manually unload the boat by inverting it over the pan. Such procedure increases the exposure of personnel to the radioactivity of the pellets, airborne particles, and high temperature of the sintering boat, so that elaborate protective safeguards must be taken. Also, with the large number of pellets being contained in a single sintering boat, the risk of chipping and otherwise damaging the valuable pellets is substantially increased.
One automated approach to unloading pellets from a sintering boat is disclosed in U.S. Pat. No. 4,642,016 to Bucher et al, assigned to the assignee of the present invention. In the Bucher et al patent, an unloading apparatus is disclosed which includes a boat clamping and inverting mechanism for carrying out a controlled, gradual tilting or pivoting of the loaded sintering boat, and a pellet transfer shroud defining a transfer surface adjacent the boat as it is tilted or pivoted through an arcuate path from an upright position to an inverted position along the transfer surface. The transfer surface is spaced from the boat path just enough to allow individual pellets, upon sliding through the open top of the boat as the boat pivots from its upright to inverted position, to slide down the transfer surface past the boat and on to the next station.
However, the approach of the above-cited patent is not particularly applicable to depositing pellets from the boat directly in a stationary transfer pan. Consequently, a need still exists for an alternative approach to unloading pellets from the sintering boat directly into the transfer pan. The technique must not only carefully handle the pellets to avoid chipping thereof, but must also gently handle the expensive, and oftentimes brittle, molybdenum sintering boat.